Amperometric lysine bioprobes analysis in feeds.

Amperometric enzyme electrode probes have been constructed for the specific determination of L-lysine and used in batch and flow analysis. The enzyme lysine oxidase was immobilized on a preactivated polymer support which was placed on a platinum electrode. Additional blocking membranes conferred high stability, reproducibility and avoided electrochemical and enzyme interferences. Parameters including pH, temperature, storage and operational times were optimized. Lysine was determined in the range 10(-6)-2.10(-3)M with a detection limit of 5 x 10(-7)M. The Michaelis constant was 2 x 10(-3)M. This value was approximately two order of magnitudes higher than that reported in literature for the free enzyme. The response time of the probe was about 2 min in batch and flow analysis and 30 sec in flow injection analysis (FIA). The resulting probes were stable for more than three months with more than 300 analyses performed. The determination of lysine was carried out by both flow-through analysis and FIA. Analysis in feeds was carried out by acid hydrolysis to liberate lysine; then the solution was analyzed by the bioprobe and HPLC procedures. Results by the two methods correlated well.